题目

Given a positive integer c, how many integers are greater than c and less than 2c?

选项

A.

B.

c

C.

c-1

D.

c-2

E.

c+1

解析

给定一个正整数\(c\),有多少个整数大于\(c\)且小于\(2c\)? - 假设\(c = 3\),那么\(2c=6\),大于\(3\)且小于\(6\)的整数有\(4\)和\(5\),共\(2\)个,而\(3 - 1=2\)。 - 假设\(c = 4\),那么\(2c = 8\),大于\(4\)且小于\(8\)的整数有\(5\)、\(6\)、\(7\),共\(3\)个,而\(4-1 = 3\)。 一般地,大于\(c\)且小于\(2c\)的整数为\(c + 1,c + 2,\cdots,2c-1\),一共有\((2c - 1)-(c + 1)+1=2c-1-c-1 + 1=c-1\)个。 所以答案是\(C\)。
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